Cyanate ester compounds produce triazine rings by curing and have high heat resistance and excellent electrical characteristics and therefore are widely used as raw materials of various functional polymer materials such as structural composite materials, adhesives, electrical insulating materials, and electrical and electronic components. However, in recent years, with an advance in required performance in these application fields, various properties required as functional polymer materials have become increasingly strict. Examples of such properties include flame retardancy, heat resistance, a low coefficiency of thermal expansion, low water-absorbing property, a low dielectric constant, a low dielectric loss tangent, weather resistance, chemical resistance, and high fracture toughness. However, functional polymer materials have not always satisfied these required properties so far.
For example, a problem in the semiconductor package material field is that with the thinning of substrates, warpage occurs due to the mismatch of the coefficiencies of thermal expansion between a semiconductor chip and a substrate material. As means for solving this, it is required to improve the low thermal expansion of the functional polymer material itself used for the substrate material.
In addition, when a halogen atom is contained in a functional polymer material, a halogen-based gas, which may cause environmental pollution, may be generated during combustion, and the insulating properties of the final product may be decreased. Further, when a phosphorus atom is contained in a functional polymer material, the required properties other than flame retardancy (heat resistance, moisture resistance, low water-absorbing property, and the like) are often declined. Therefore, it is also required to improve the flame retardancy of the functional polymer material itself without containing a halogen atom or a phosphorus atom.
Further, when a laminate for printed wiring board applications and the like is produced, the step of making a prepreg by first dissolving a precursor of a functional polymer material in a solvent such as methyl ethyl ketone to prepare a varnish, then impregnating a glass cloth with the varnish, and drying it is adopted. Therefore, it is also required to improve the solvent solubility of the monomer before curing that is the precursor of the functional polymer material.
As an example in which a hardened product of a single cyanate ester compound having low thermal expansion is obtained, the use of a bifunctional cyanatophenyl-based cyanate ester compound in which the hydrogen of a methylene group bonding cyanatophenyl groups to each other is replaced by a particular alkyl group (1,1-bis(4-cyanatophenyl)isobutane) is proposed (for example, see Patent Document 1).
As an example in which a hardened product of a single cyanate ester compound having low thermal expansion and flame retardancy is obtained, the use of a cyanate ester compound having an aralkyl structure is proposed (for example, see Patent Document 2).
As an example in which a hardened product of a single cyanate ester compound having lower water-absorbing property than a novolac-based cyanate ester compound is obtained, the use of a cyanate ester compound referred to as an APT resin (a cyanate ester compound obtained by cyanating a resin synthesized from diphenyl ether, formaldehyde, and phenol) is proposed (for example, see Patent Document 3).